ABSTRACT This Clinical Core will implement first in human PET imaging with new radiotracers targeting ?-synuclein (?-syn) and 4 repeat tau (4R tau). Radiotracers will be developed pre-clinically in the Med Chem Core and in Projects 1 and 2 focusing on ?-syn and 4R tau, respectively. We will focus ?-syn radiotracers on two synucleinopathies, Parkinson disease (PD) and Multiple Systems Atrophy (MSA), and focus 4R tau radiotracers on two different tauopathies, progressive supranuclear palsy (PSP) and familial frontotemporal dementias (FTD) due to mutation in Microtubule Associated Protein Tau (MAPT) gene. We will draw participants and interact with multiple ongoing clinical cohorts of FTD, PSP, PD and MSA. The Clinical Core functions include interaction with the Executive Committee to determine when to start human studies, coordinate required regulatory activities for radiotracer candidates, carry out early safety assessments including whole body dosimetry studies at Penn; coordinate patient selection criteria, centrally collect and serve all imaging and demographic data, coordinate tracer kinetic methods development and validation for human imaging, and coordinate all data to efficiently enable GO-NOGO decisions for candidate radiotracers. Radiotracers for ?-syn will be tested in two different synucleinopathies, PD and MSA whereas, 4R tau radiotracers will be tested in PSP and FTD patients. As a final check on diagnosis and specificity of candidate radiotracers, we will request all patient participants to permit postmortem brain donation for autoradiography of relevant radiotracers on fresh frozen brain tissues. Additionally, this Core will interact with multiple ongoing studies with cohorts studying PD, MSA, PSP and FTD. Finally, a robust data sharing plan facilitates collaboration and use of support documents and imaging data.